The use of Laser Powder Bed Fusion (L-PBF) process inevitably generates defects (lack of fusion, gas pores) which have significant impact on the fatigue behavior. The consideration of such defects is therefore an important challenge for a safe design of additively manufactured components against fatigue. In the present study, fatigue specimens with different defect populations have been obtained by varying the process parameters. These specimens have been subjected to fatigue tests under multiaxial loading conditions (tension, torsion, and combined tension-torsion) in the High Cycle Fatigue regime. A Kitagawa-Takahashi diagram was determined for each loading type, describing the evolution of the fatigue strength at 1 x 10⁶ cycles with respect to the defect size. These results evidenced that the sensitivity to the defects depends on the loading type, torsion dominated loadings being less sensitive to the defect size than tension dominated ones. In addition, a numerical methodology aiming at predicting the fatigue strength from finite-element (FE) simulations was proposed, considering explicitly the geometry of L-PBF defects, or idealized defect shapes.  It was found that the experimental results can be satisfyingly reproduced using synthetic ellipsoidal defects.

Keywords: Multiaxial fatigue; Defect; L-PBF